EQLS 2012 - Sampling

Sampling design

The sample of the EQLS is representative of the adult population living in private households during the fieldwork period in each of the countries covered. In most countries, multi-stage stratified and clustered sampling design was applied.

The main sampling stages are as follows:Selection of primary sampling units (PSUs), stratified according to geographic regions (at NUTS2 level or equivalent) and degree of urbanisation. Addresses were clustered in a defined number of PSUs except in the Netherlands, Malta, and Sweden where samples were drawn directly from the registries without clustering.

Subsequently, individuals or addresses were randomly selected in each PSU. In 15 countries, up-to-date, high quality address or population registers covering at least 95% of persons or households were available and these were used as a sampling frame. Random route sampling was used in 12 countries where access to register information of sufficient quality was not available., In those countries where the random route method was applied, enumeration of addresses was carried out and validated separately in advance of fieldwork to improve the survey quality.

Selection of an interviewee within a household: Once a contact with a household was established, the interviewer followed a defined and documented procedure of respondent selection by firstly registering all adults in the household, and then applying the ‘next birthday rule’ for selecting a person to be interviewed. Only the selected person could be interviewed and only one person per household. The next birthday rule was not necessary in Hungary, Malta, Slovenia and Sweden, where individual respondents were preselected from the name-based registries.

To increase the chance of successful contact and interviewing a randomly sampled person, at least four visits to a preselected address at different times of the day and of the week, spread over at least two weeks, were carried out.

Due to the geographical spread and expected difficulties in achieving collaboration through initial face-to-face contacts, telephone pre-recruitment of respondents was allowed in Finland and Sweden. Only those who agreed on the telephone to participate in the survey were visited by interviewers.

Sample size

The sample size ranges from 1,001 to 3,055 with the target number of interviews set at 1,000 interviews for most countries. The seven EU countries with the largest population, making up altogether three quarters of the EU population, had a higher sample size in order to help to improve the precision of estimates at European as well as national level. The total sample size for all 34 countries was 43,636.